1. Field of the Invention
This invention relates to a semiconductor device and a manufacturing method thereof and more particularly to a semiconductor device having a semiconductor chip bonded on a radiator plate with interposition of a bonding layer.
2. Description of the Related Art
It has been required that consumer appliances are made compact and the requirement has called for one chip structuring of a semiconductor device or high density mounting of a semiconductor device, and thus area array packages such as ball grid array, in which external connecting terminals are arranged in the form of two-dimensional area (referred to simply as "BGA" hereinafter), and land grid array (referred to simply as "LGA" hereinafter) have been proposed and practically used to satisfy the requirement for multi-pin semiconductor.
As a related area package, tape BGA (Tape-BFA, referred to simply as "T-BGA" hereinafter), in which TAB (Tape Automated Bonding) is used as interconnection technique, is described referring to FIG. 2.
For example, a semiconductor chip 44 is bonded on a radiator plate 40 consisting of copper material with interposition of a paste bonding layer 42. Many electrode pads 46 are formed on the surface of the semiconductor chip 44.
On the circumference of the radiator plate 40 surrounding the semiconductor chip 44, a stiffener 50 is bonded with interposition of a bonding layer 48. On the stiffener 50, many external connecting terminals 54 having a ball-shaped end respectively are arranged dispersedly in the form of array.
These many external connecting terminals 54 are connected to the electrode pads on the semiconductor chip 44 with interposition of respective inner leads 56. These many external connecting terminals 54 are covered with an insulating film 58 excepting the ball-shaped ends and insulated stably each other. As described herein above, the external connecting terminals 54, inner leads 56, and insulating film 58 constitute a wiring pattern 60 for connecting the electrode pads of the semiconductor chip 44 to the external.
The semiconductor chip 44 bonded on the radiator plate 40 with interposition of the paste bonding layer 42 and the inner leads 56 connected to the electrode pads 46 are covered with sealing resin 62, this is so-called resin sealing.
As described herein above, in the T-BGA, because many external connecting terminals 54 are arranged dispersedly in the form of array on the stiffener 50 surrounding the semiconductor chip 44, the package size of a T-BGA is made small even if the pitch of the external connecting terminals 54 of the semiconductor device having many pins is relatively large, for example, 1.0 mm or 0.27 mm, therefore this structure is effective for high density mounting.
Further, the semiconductor chip 44 is bonded directly on the radiator plate 40 with interposition of the paste bonding layer 42, and therefore heat generated from the semiconductor element during operation is easily dissipated, thus this structure is also effective for low heat resistance packaging.
However, in the above-mentioned T-BGA, the thermal expansion coefficient of the semiconductor chip 44 is approximately 3 ppm/.degree. C. and the thermal expansion coefficient of the radiator plate 40 consisting of copper material is approximately 17 ppm/.degree. C., the large difference in the thermal expansion coefficient between both components causes the stress concentration on the paste bonding layer 42 between the semiconductor chip 44 and the radiator plate 40, for example, when the semiconductor device is subjected to a thermal cycle test (referred to simply as T/C test hereinafter), in which the temperature of the T-BGA is varied cyclically, the bonding strength of the paste bonding layer 42 is decreased to cause cracking or separation occasionally at the end.
As described herein above, though the semiconductor device is excellent in heat dissipation initially as it is fabricated, after T/C test, the bonding strength of the paste bonding layer 42 which has been subjected to stress concentration is decreased, and good contact between the semiconductor chip 44 and the radiator plate 40 is deteriorated to result in significantly reduced heat dissipation, and thus the reliability in endurance becomes poor disadvantageously.
Not only T-BGA but also semiconductors of other types as long as a bonding layer is provided between a semiconductor chip and a radiator plate or a die pad consisting of copper material are involved generally in the problem.